ESR1 and breast cancer: It is noteworthy that up to date, only few ESR1 fusions (ESR1-e2>CCDC170, ESR1-e4>CCDC170, ESR1-e5>CCDC170, ESR1-e6>NOP2, ESR1-e6>AKR1D1, ESR1-e6>POLH) were detected in primary breast cancer samples (Table 1).